A literature review and test: Structure and physicochemical properties of spinel LiMn2O4 synthesized by different temperatures for lithium ion battery

A series of LiMn₂O₄ spinel was prepared by adipic acid-assisted sol–gel method at different temperatures. The structure and physicochemical properties of spinel LiMn₂O₄ synthesized by different temperatures were investigated by differential thermal analysis (DTA) and thermogravimetery (TG), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron micrographs (SEM), inductively coupled plasma-mass spectroscopy (ICP-MS), galvanostatic charge–discharge test, and cyclic voltammetry (CV), respectively. TG–DTA shows that the weight loss occurs in four temperature regions during the synthesis of LiMn₂O₄. XRD indicates that the sintering temperature affects the formation of spinel phase, and prominent LiMn₂O₄ spinel powder with smaller atom location confusion forms about 800 °C. XPS reveals that the manganese oxidation state in spinel lithium manganese oxide synthesized at different temperatures is between +3 and +4. SEM shows that LiMn₂O₄ spinel synthesized at 800 °C has the uniform, nearly cubic structure morphology with narrow size distribution. ICP-MS indicates that the average chemical valence of Mn element of LiMn₂O₄ synthesized at 800 °C is the most close to 3.5 among the samples synthesized at different temperatures. CV illustrates that the LiMn₂O₄ synthesized at 800 °C has the best electrochemical activity. Charge–discharge test explains that the capacity retention sintered at 350, 700 and 800 °C over the first 50 cycles is 93.6%, 86.1% and 85.2%, respectively, but the discharge capacity at the 50th cycle is 82.2, 104.8 and 110.8 mAh g⁻¹, respectively.     

Effects of protecting layer [Li,La]TiO3 on electrochemical properties of LiMn2O4 for lithium batteries

A sample of LiMn₂O₄ spinel oxide was surface-modified with lithium lanthanum titanate ([Li,La]TiO₃), which was developed as a lithium ionic conductor, by means of hydrothermal processing and subsequent heat treatment at 400 °C. The surface coating layers were analyzed by morphology observation using a transmission electron microscopy. Energy-dispersive spectrometry and X-ray photoelectron spectroscopy were used for element investigation. The surface modification effects on rate capability during cycling and capacity retention for the LiMn₂O₄ spinel oxide were confirmed. Then Mn dissolution during storage at elevated temperatures of the pristine, coated sample was characterized. The Mn dissolution characterization was based on the idea that Mn dissolution is one of the most significant reasons for capacity loss for LiMn₂O₄ spinel oxide, and this phenomenon is especially severe at elevated temperatures. Our experimental results indicate that the surface-modified sample shows much a better initial capacity and rate capability compared with the pristine sample. The [Li,La]TiO₃ coating effectively enhances the structural stability of LiMn₂O₄ at elevated temperatures, most likely because the [Li,La]TiO₃-modifying layers play a definitive role in suppressing Mn dissolution in the electrolyte during storage.     

Synthesis, structural and magnetic characterization of nanocrystalline nickel ferrite—NiFe2O4 obtained by reactive milling

Nanocrystalline nickel ferrite (NiFe₂O₄) has been synthesized from a stoichiometric mixture of oxides NiO and α-Fe₂O₃ in a high energy planetary mill. An annealing at 350 °C, after milling, was used to improve the solid state reaction. The obtained powders were investigated by X-ray diffraction, magnetic measurements, scanning electron microscopy, X-ray microanalysis and differential scanning calorimetry. The particles size distribution was analyzed using a laser particle size analyser. The nickel ferrite begins to form after 4 h of milling and continuously form up to 16 h of milling. The obtained nickel ferrite has many inhomogeneities and a distorted spinel structure. The mean crystallites size at the final time of milling is 9 ± 2 nm and the lattice parameter increases with increase the milling time. DSC measurements revealed a large exothermic peak associated with cations reordering in the crystalline structure. The magnetization of the obtained powder depends on the milling time and annealing. After the complete reaction between the starting oxides the milling reduces the magnetization of the samples. The magnetization increases after annealing, due to the reorganization of the cations into the spinel structure.     

Characterization and electrochemical properties of carbon-coated Li4Ti5O12 prepared by a citric acid sol-gel method

Since carbon coating can effectively improve electrical wiring of Li₄Ti₅O₁₂ and thus enhance its high rate performance, a novel and simple citric acid sol-gel method for in situ carbon coating is employed in this study. The effects of the amount of the carbon source in the starting xerogel on the particle size, the resistance and the electrochemical performance of the synthesized Li₄Ti₅O₁₂ samples are systematically studied. The physical and electrochemical properties of the obtained samples have been characterized by XRD, TG-DSC, SEM, TEM, BET, A.C. impedance, galvanostatically charge-discharge and cyclic voltammetry tests. The results show that the initial amount of the carbon source in the starting xerogel is a critical factor which determines the content of the coated carbon and the pore volume, therefore governs the high rate performance of the Li₄Ti₅O₁₂/C composites. The Li₄Ti₅O₁₂/C composite with in situ carbon coating of 3.5 wt% exhibits the best electrochemical performance which delivers delithiation capacities of 143.6 and 133.5 mAh g⁻¹ with fairly stable cycling performance even after 50 cycles at 0.5C and 1C rate, respectively.     

Al2O3-nanodiamond composite coatings with high durability and hydrophobicity prepared by aerosol deposition

We attempted the room-temperature fabrication of Al₂O₃-based nanodiamond (ND) composite coating films on glass substrates by an aerosol deposition (AD) process to improve the anti-scratch and anti-smudge properties of the films. Submicron Al₂O₃ powder capable of fabricating transparent hard coating films was used as a base material for the starting powders, and ND treated by 1H,1H,2H,2H-perfluorooctyltriethoxysilane (PFOTES) was added to the Al₂O₃ to increase the hydrophobicity and anti-wear properties. The ND powder treated by PFOTES was mixed with the Al₂O₃ powder by ball milling to ratios of 0.01 wt.%, 0.03 wt.%, and 0.05 wt.% ND. The water contact angle (CA) of the Al₂O₃-ND composite coating films was increased as the ND ratio increased, and the maximum water CA among all the films was 110°. In contrast to the water CA, the Al₂O₃-ND composite coating films showed low transmittance values of below 50% at a wavelength of 550 nm due to the strong agglomeration of ND. To prevent the agglomeration of ND, the starting powders were mixed by attrition milling. As a result, Al₂O₃-ND composite coating films were produced that showed high transmittance values of close to 80%, even though the starting powder included 1.0 wt.% ND. In addition, the Al₂O₃-ND composite coating films had a high water CA of 109° and superior anti-wear properties compared to those of glass substrates.     

Phase constituents and microstructure of laser cladding Al2O3/Ti3Al reinforced ceramic layer on titanium alloy

Laser cladding of the Fe₃Al + TiB₂/Al₂O₃ pre-placed alloy powder on Ti-6Al-4V alloy can form the Ti₃Al/Fe₃Al + TiB₂/Al₂O₃ ceramic layer, which can greatly increase wear resistance of titanium alloy. In this study, the Ti₃Al/Fe₃Al + TiB₂/Al₂O₃ ceramic layer has been researched by means of electron probe, X-ray diffraction, scanning electron microscope and micro-analyzer. In cladding process, Al₂O₃ can react with TiB₂ leading to formation of amount of Ti₃Al and B. This principle can be used to improve the Fe₃Al + TiB₂ laser cladded coating, it was found that with addition of Al₂O₃, the microstructure performance and micro-hardness of the coating was obviously improved due to the action of the Al-Ti-B system and hard phases.     

Synthesis and electrochemical properties of Li4Ti5O12

The spinel compound Li₄Ti₅O₁₂ was synthesized by a solid state method. In this synthesizing process, anatase TiO₂ and Li₂CO₃ were used as reactants. The influences of reaction temperature and calcination time on the properties of products were studied. When calcination temperature was 750 °C and calcination temperature was 24 h, the products exhibited good electrochemical properties. Its discharge capacity reached 160 mAh g⁻¹ and its capacity retention was 97% at the 50th cycle when the current rate was 1 C. When current rate increased to 10 C, its first discharge capacity could reach 136 mAh g⁻¹, and its capacity retention was 85% at the 50th cycle.     

Oxidation resistance of TiAl3-Al composite coating on orthorhombic Ti2AlNb based alloy

The TiAl₃-Al composite coating on orthorhombic Ti₂AlNb based alloy was prepared by cold spray. Oxidation in air at 950 °C indicated that the bare alloy exhibited poor oxidation resistance due to the formation of TiO₂/AlNbO₄ mixture and intended to scale off at the TiO₂ rich zone. A nitride layer about 2 µm was formed under the oxide layer. The oxygen invaded deeply into the alloy and caused severe microhardness enhancement in the near surface region. The TiAl₃-Al composite coating exhibited parabolic oxidation kinetics and showed no sign of degradation after oxidized up to 1098 h at 950 °C in air under quasi-isothermal condition. No scaling of the coating was observed after oxidized at 950 °C up to the tested 150 cycles. The major oxide in the oxidized coating was Al₂O₃. The AlTi₂N, TiAl and small amount of TiO₂ were also observed in the oxidized coating. The EPMA and microhardness tests showed that inward oxygen diffusion was prevented by the interlayer, which was formed between the composite coating and the substrate during heat-treatment. Microstructure analyses demonstrated that the interlayer play a major role in protecting the substrate alloy from high temperature oxidation and interstitial embrittlement.     

Vitreous phase coating on glaserite-type alkaline earth silicate blue phosphor BaCa2MgSi2O8:Eu

A simple solid-state reaction was used to apply a vitreous-phase coating onto Eu²⁺-doped BaCa₂MgSi₂O₈ blue-phosphor particles. The vitreous phase was generated by liquid phase sintering at 1200 °C. The coated phosphor exhibited resistant to an acid dispersant. When a small amount of Al and La was added in raw materials, they were incorporated in the vitreous coating phase.     

Synthesis, structure, and properties of Li2Pb2CuB4O10 with isolated [CuB4O10] units

The copper borate Li₂Pb₂CuB₄O₁₀ has been synthesized in air by the standard solid-state reaction at temperature in the range 550-650 °C and the structure of Li₂Pb₂CuB₄O₁₀ was determined by single-crystal X-ray diffraction. Li₂Pb₂CuB₄O₁₀ crystallizes in the monoclinic space group C2/c (no. 15) with a = 16.8419(12), b = 4.7895(4), c = 13.8976(10) Å, and β = 125.3620(10)°, V = 914.22(12) Å³, and Z = 4, as determined by single-crystal X-ray diffraction. The Li₂Pb₂CuB₄O₁₀ structure exhibits isolated units of stoichiometry [CuB₄O₁₀]⁶⁻ that are built from CuO₄ distorted square planes and triangular BO₃ groups. The IR spectroscopy and thermal analysis investigations of Li₂Pb₂CuB₄O₁₀ are also presented.     

Direct synthesis of Fe3O4 nanopowder by thermal decomposition of Fe-urea complex and its properties

An easy synthesis route of magnetite (Fe₃O₄) nanopowder is developed by using thermal decomposition of Fe-urea complex ([Fe(CON₂H₄)₆](NO₃)₃). The formation of Fe₃O₄ is confirmed from X-ray powder diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) measurements. The morphological properties and magnetic properties of the Fe₃O₄ are characterized by transmission electron microscopy (TEM) and magnetic measurements, respectively. By an increase in reaction temperature from 200 to 300 °C, the average crystallite size of the Fe₃O₄ nanopowder increases from 37 to 50 nm. Room temperature magnetization hysteresis curves show that the Fe₃O₄ nanopowder possesses ferrimagnetic characteristics. The saturation magnetization of the Fe₃O₄ nanopowder increases from 70.7 to 89.1 emu/g when the reaction temperature increases from 200 to 300 °C.     

Microwave synthesis, structure, and magnetic properties of quasi-one-dimensional complex oxide Sr4LiMn2O9

The complex oxide Sr₄LiMn₂O₉ belonging to the A_3n+3mA′_nMn_3m+nO_9m+6n family (m = 3, n = 1) was prepared from a mixture of SrCO₃ and LiMn₂O₄ in a microwave furnace by the solid state reaction. The results of structural refinements and magnetic properties are presented. The crystal structure of Sr₄LiMn₂O₉ was solved using simultaneously X-ray and neutron diffraction data with the GSAS program in the space group P321 with unit cell parameters: a = 9.5721(7) Å, c = 7.8264(5) Å, V = 621.025 Å³, Z = 3. Sr₄LiMn₂O₉ was found to contain 2 independent 1D chains of face-shared polyhedrons with a sequence of two octahedrons and one trigonal prism. The chains are separated by strontium cations. The refinement results show that the octahedrons and trigonal prisms in the first chain orderly contain Mn and Li, respectively, whereas the second chain is characterized by mixed occupation of these structural positions. The temperature dependence of the magnetic susceptibility of Sr₄LiMn₂O₉ was found to be due to antiferromagnetically coupled dimers from magnetic Mn cations.     

Synthesis and electrochemical properties of porous LiV3O8 as cathode materials for lithium-ion batteries

In this paper, we report on the synthesis of porous LiV₃O₈ by using a tartaric acid-assisted sol-gel process and their enhanced electrochemical properties for reversible lithium storage. The crystal structure, morphology and pore texture of the as-synthesized samples are characterized by means of XRD, SEM, TEM/HRTEM and N₂ adsorption/desorption measurements. The results show that the tartaric acid plays a pore-making function and the calcination temperature is an important influential factor to the pore texture. In particular, the porous LiV₃O₈ calcined at 300 °C (LiV₃O₈-300) exhibits hierarchical porous structure with high surface area of 152.4 m² g⁻¹. The electrochemical performance of the as-prepared porous LiV₃O₈ as cathode materials for lithium ion batteries is investigated by galvanostatic charge-discharge cycling and electrochemical impedance spectroscopy. The porous LiV₃O₈-300 displays a maximum discharge capacity of 320 mAh g⁻¹ and remains 96.3% of its initial discharge capacity after 50 charge/discharge cycles at the current density of 40 mA g⁻¹ due to the enhanced charge transfer kinetics with a low apparent activity energy of 35.2 kJ mol⁻¹, suggesting its promising application as the cathode material of Li-ion batteries.     

Investigation on 3-dimensional carbon foams/LiFePO4 composites as function of the annealing time under inert atmosphere

The morphological and electrochemical investigation of 3-dimensional (3D) carbon foams coated with olivine structured lithium iron phosphate as function of the annealing time under nitrogen atmosphere is reported. The LiFePO₄ as cathode material for lithium ion batteries was prepared by a Pechini-assisted sol-gel process. The coating has been successfully performed on commercially available 3D-carbon foams by soaking in aqueous solution containing lithium, iron salts and phosphates at 70 °C for 2-4 h. After drying-out, the composites were annealed at 600 °C for different times ranging from 0.4 to 10 h under nitrogen. The formation of the olivine-like structured LiFePO₄ was confirmed by X-ray diffraction analysis performed on the powder prepared under similar conditions. The surface investigation of the prepared composites showed the formation of a homogeneous coating by LiFePO₄ on the foams. The cyclic voltammetry curves of the composites show an enhancement of electrode reaction reversibility by increasing the annealing time. The electrochemical measurements on the composites showed good performances delivering a discharge specific capacity of 85 mAh g⁻¹ at a discharging rate of C/25 at room temperature after annealing for 0.4 h and 105 mAh g⁻¹ after annealing for 5 h.     

Synthesis of nanocrystalline nickel-zinc ferrite (Ni0.8Zn0.2Fe2O4) thin films by chemical bath deposition method

The nickel-zinc ferrite (Ni_0.8Zn_0.2Fe₂O₄) thin films have been successfully deposited on stainless steel substrates using a chemical bath deposition method from alkaline bath. The films were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), static water contact angle and cyclic voltammetry measurements. The X-ray diffraction pattern shows that deposited Ni_0.8Zn_0.2Fe₂O₄ thin films were oriented along (3 1 1) plane. The FTIR spectra showed strong absorption peaks around 600 cm⁻¹ which are typical for cubic spinel crystal structure. SEM study revealed compact flakes like morphology having thickness ∼1.8 μm after air annealing. The annealed films were super hydrophilic in nature having a static water contact angle (θ) of 5°.The electrochemical supercapacitor study of Ni_0.8Zn_0.2Fe₂O₄ thin films has been carried out in 6 M KOH electrolyte.The values of interfacial and specific capacitances obtained were 0.0285 F cm⁻² and 19 F g⁻¹, respectively.     

SmBaCoCuO5+x as cathode material based on GDC electrolyte for intermediate-temperature solid oxide fuel cells

The performance of SmBaCoCuO_5+x (SBCCO) cathode has been investigated for their potential utilization in intermediate-temperature solid oxide fuel cells (IT-SOFCs). The powder X-ray diffraction (XRD), thermal expansion and electrochemical performance on Ce_0.9Gd_0.1O_1.95 (GDC) electrolyte are evaluated. XRD results show that there is no chemical reaction between SBCCO cathode and GDC electrolyte when the temperature is below 950 °C. The thermal expansion coefficient (TEC) value of SBCCO is 15.53 × 10⁻⁶ K⁻¹, which is ∼23% lower than the TEC of the SmBaCo₂O_5+x (SBCO) sample. The electrochemical impedance spectra reveals that SBCCO symmetrical half-cells by sintering at 950 °C has the best electrochemical performance and the area specific resistance (ASR) of SBCCO cathode is as low as 0.086 Ω cm² at 800 °C. An electrolyte-supported fuel cell generates good performance with the maximum power density of 517 mW cm⁻² at 800 °C in H₂. Preliminary results indicate that SBCCO is promising as a cathode for IT-SOFCs.     

Chemical synthesis and electrochemical analysis of nickel cobaltite nanostructures for supercapacitor applications

Nickel cobaltite (NiCo₂O₄) films containing nanorods and nanoflakes are synthesized on indium tin oxide (ITO) substrates by a chemical bath deposition method and calcination process at 300 °C for 3 h. The NiCo₂O₄/ITO films are used as electrodes for supercapacitor applications, and electrochemical properties of the NiCo₂O₄ nanostructures are examined by cyclic voltammetry and charge-discharge experiments. NiCo₂O₄ nanorods exhibit the largest specific capacitance, with a value of 490 F g⁻¹at energy and power densities of 45 Wh kg⁻¹ and 2 kW kg⁻¹, respectively. This is significantly better than the performance of NiCo₂O₄ nanoflakes. Cycle-life tests show that the specific capacitance of NiCo₂O₄ is stable even after 1000 cycles, indicating its high potential for supercapacitor applications. The low cost and environmental friendliness of NiCo₂O₄ nanorods, coupled with its high supercapacitor performance, offer advantages over other transition metal oxides used for supercapacitors.     

Fabrication and properties of Ba(Zr1−xCex)0.9Y0.1O2.95/NaCl composite electrolyte materials

Ba(Zr_1−xCe_x)_0.9Y_0.1O_2.95/NaCl (x = 0.1, 0.2 and 0.3) composite electrolyte materials were fabricated with ZnO as sintering aid. The effect of ZnO on the properties of Ba(Zr_1−xCe_x)_0.9Y_0.1O_2.95 matrix were investigated. The phase composition and microstructure of samples were characterized by XRD and SEM, respectively. The electrochemical performances were studied by three-probe conductivity measurement and AC impedance spectroscopy. XRD results showed that Ba(Zr_1−xCe_x)_0.9Y_0.1O_2.95 with 2 mol% of ZnO was perovskite structure. The relative density of this sample was above 95% when sintered at 1450 °C for 6 h. By adding 10 mol% of NaCl to Ba(Zr_1−xCe_x)_0.9Y_0.1O_2.95 with 2 mol% of ZnO that was sintered at 1400 °C for 6 h, the conductivity was increased. The electrical conductivity of 1.26 × 10⁻² S/cm and activation energy of 0.23 eV were obtained when tested at 800 °C in wet hydrogen.     

Synthesis, structure and optical properties of CoAl2O4 spinel nanocrystals

CoAl₂O₄ nanocrystals were synthesized by sol-gel method using citric acid as a chelating agent at low temperature. The as-synthesized samples were characterized by thermal analysis, X-ray powder diffraction, infrared spectroscopy and transmission electron microscopy. The results show that CoAl₂O₄ spinel is the only crystalline phase with a size of 10-30 nm in the temperature range 500-1000 °C. The temperature dependence of the distribution of Al³⁺ and Co²⁺ ions in the octahedral and tetrahedral sites in nanocrystals was investigated by X-ray photoelectron spectroscopy (XPS). It is observed that the inversion parameter decreases with increasing annealing temperature. Analysis of the absorption properties indicates that Co²⁺ ions are located in the tetrahedral sites as well as in the octahedral sites in the CoAl₂O₄ nanocrystals. The origin of the green color (300-500 nm absorption band) should be due to the octahedrally coordinated Co²⁺ ions.